The present invention relates to automotive temperature sensors, and is further related to flexible circuits, wherein the flexible circuit serves as a substrate for the temperature sensor.
Temperature sensors are utilized to monitor a variety of automotive systems, including for example coolant temperature and exhaust gas temperature. These sensors typically utilize a wire-type thermistor which is generally soldered to hard-wired leads. Unfortunately, the various automotive applications for temperature sensors precludes a xe2x80x9cone fits allxe2x80x9d temperature sensor. The multiplicity of temperature sensor types also, therefore, necessitates that each type be uniquely manufactured with little chance for exchange of parts or manufacturing specifications. Major barriers to cost-reduction and/or innovation in automotive temperature sensors are the high terminal tooling costs, high lead-time and cost to make design changes, labor intensity of manufacture, and inability to integrate electronics into the design.
Flexible circuits are well known in the electrical arts, wherein a flexible insulative substrate is printed with flexible electrical circuits, typically in the form of a plurality of elongated, narrow copper traces. If somehow flexible circuit technology could be mated to temperature sensors, it would become possible to provide temperature sensors which over come the above described disadvantages.
In the art it is known to use surface-mount devices on flexible printed circuits either for temperature sensing for heating, ventilation and air conditioning (HVAC) or temperature compensation, and such devices are made by Delphi-Packard and Berlin. However, these passenger compartment devices are not intended for an xe2x80x9cunder the hoodxe2x80x9d environment.
The present invention is a temperature sensor incorporating flexible circuit technology which allows for replacement of costly wires and lead-frames of the prior art with a generic substrate that commonizes parts, processes, and tooling, as well as enabling electronics integration.
The temperature sensor according to the present invention includes a flexible circuit sensor subassembly composed of a flexible printed circuit substrate on which is printed a sensor circuit. In a preferred example the flexible circuit sensor subassembly, the sensor circuit has a sensor at a distal end, as for example a surface mount device (SMD) thermistor, a plurality of trace pads at a proximate end, and an interconnecting conductive trace between each trace pad and the sensor. A crimp terminal is respectively crimped onto each trace pad to provide a flexible circuit sensor assembly, wherein the crimp terminals are configured as needed for interfacing with an external circuit. The location of the sensor may be selectively located anywhere on the conductive traces to thereby easily size the probe length of the flexible circuit sensor subassembly to suit a any particular application and fit into any housing.
Accordingly, the apparatus for manufacturing the flexible circuit sensor assembly can provide variously configured assemblies, each having particular R-T characteristics, connection systems and probe lengths. Indeed, new parts with custom flexible circuit assemblies can be run with very little tooling investment. The manufacturing process is amenable to automation, and low volume production can be run profitably.
A housing is formed over the flexible circuit sensor assembly. For example, a plastic injection molding process encapsulates the thermistor circuit and fixedly locates the pins of the crimp terminals. The housing either alone or located in an external shell provides a temperature sensor for a particular purpose.
In a variation of the flexible circuit sensor assembly, electronic components can be integrated with the sensor circuit to provide a smart sensor circuit, which may include multiple sensing devices.
Accordingly, it is an object of the present invention to provide a temperature sensor which incorporates flexible printed circuit technology.
This, and additional objects, advantages, features and benefits of the present invention will become apparent from the following specification.